Rechargeable electric storage batteries are commercially available in a wide range of sizes for use in a variety of applications. As battery technology continues to improve, batteries find new applications which impose increasingly stringent specifications relating to physical size and performance. Thus, new technologies have yielded smaller and lighter weight batteries having longer storage lives and higher energy output capabilities enabling them to be used in an increasing range of applications, including medical applications, where, for example, the battery can be used in a medical device which is implanted in a patient's body. Such medical devices can be used to monitor and/or treat various medical conditions.
Batteries for implantable medical devices are subject to very demanding requirements, including long useful life, high power output, low self-discharge rates, compact size, high reliability over a long time period, compatibility with the patient's internal body chemistry, etc. Although various battery chemistries have been tried, lithium ion technology is generally accepted as the preferred chemistry for medical implant applications.
Such electric storage batteries are generally comprised of a tubular metal case enveloping an interior cavity which contains an electrode assembly surrounded by a suitable electrolyte. The electrode assembly generally comprises a plurality of positive electrode, negative electrode, and separator layers which are typically stacked and/or spirally wound to form a jellyroll. The positive electrode is generally formed of a metal substrate having positive active material coated on both faces of the substrate. Similarly, the negative electrode is formed of a metal substrate having negative active material coated on both faces of the substrate. In forming an electrode assembly, separator layers are interleaved between the positive and negative electrode layers to provide electrical isolation.